U.S. patent application number 14/560039 was filed with the patent office on 2016-06-09 for hydrocarbon resource heating system including choke fluid dispenser and related methods.
The applicant listed for this patent is HARRIS CORPORATION. Invention is credited to Murray Hann, Verlin Hibner, Mark TRAUTMAN, Brian Wright.
Application Number | 20160160622 14/560039 |
Document ID | / |
Family ID | 56087593 |
Filed Date | 2016-06-09 |
United States Patent
Application |
20160160622 |
Kind Code |
A1 |
TRAUTMAN; Mark ; et
al. |
June 9, 2016 |
HYDROCARBON RESOURCE HEATING SYSTEM INCLUDING CHOKE FLUID DISPENSER
AND RELATED METHODS
Abstract
A system for heating a hydrocarbon resource in a subterranean
formation having a wellbore extending therein may include a radio
frequency (RF) source, a choke fluid source, and an elongate RF
antenna configured to be positioned within the wellbore and coupled
to the RF source, with the elongate RF antenna having a proximal
end and a distal end separated from the proximal end. The system
may also include a choke fluid dispenser coupled to the choke fluid
source and positioned to selectively dispense choke fluid into
adjacent portions of the subterranean formation at the proximal end
of the RF antenna to define a common mode current choke at the
proximal end of the RF antenna.
Inventors: |
TRAUTMAN; Mark; (Melbourne,
FL) ; Hibner; Verlin; (Melbourne Beach, FL) ;
Hann; Murray; (Malabar, FL) ; Wright; Brian;
(Indiatlantic, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HARRIS CORPORATION |
Melbourne |
FL |
US |
|
|
Family ID: |
56087593 |
Appl. No.: |
14/560039 |
Filed: |
December 4, 2014 |
Current U.S.
Class: |
166/302 ;
166/332.6; 166/57 |
Current CPC
Class: |
E21B 36/04 20130101;
E21B 43/2408 20130101; E21B 43/2401 20130101; E21B 36/00 20130101;
E21B 34/12 20130101 |
International
Class: |
E21B 43/24 20060101
E21B043/24; E21B 34/12 20060101 E21B034/12; E21B 36/00 20060101
E21B036/00 |
Claims
1. A system for heating a hydrocarbon resource in a subterranean
formation having a wellbore extending therein, the system
comprising: a radio frequency (RF) source; a choke fluid source; an
elongate RF antenna configured to be positioned within the wellbore
and coupled to said RF source, said elongate RF antenna having a
proximal end and a distal end separated from the proximal end; and
a choke fluid dispenser coupled to said choke fluid source and
positioned to selectively dispense choke fluid into adjacent
portions of the subterranean formation at the proximal end of said
RF antenna to define a common mode current choke at the proximal
end of said RF antenna.
2. The system of claim 1 wherein the choke fluid comprises an
electrical conductivity enhancing fluid.
3. The system of claim 1 wherein the choke fluid comprises
water.
4. The system of claim 1 wherein said RF antenna comprises a
cylindrical conductor; and further comprising an RF transmission
line extending at least partially within said cylindrical conductor
and coupling said RF source to said RF antenna.
5. The system of claim 4 wherein said choke fluid dispenser is
carried by said transmission line and comprises: an inner sleeve
surrounding said RF transmission line; a liner surrounding said
inner sleeve and defining a first annular chamber therewith, said
liner having a plurality of ports therein in fluid communication
with said choke fluid source; and an outer sleeve surrounding said
liner and defining a second annular chamber therewith to receive
choke fluid from the plurality of ports, said outer sleeve having a
plurality of openings therein to pass choke fluid from the annular
chamber into the subterranean formation adjacent the antenna.
6. The system of claim 5 wherein said inner sleeve is slidably
movable with respect to said liner; and wherein said liner is fixed
to said outer sleeve.
7. The system of claim 4 further comprising a magnetic choke to be
coupled to said transmission line and spaced apart from said choke
fluid dispenser within the wellbore.
8. The system of claim 1 wherein said choke fluid dispenser further
comprises a respective seal at each opposing end of said inner
sleeve.
9. The system of claim 1 wherein said RF antenna comprises a
cylindrical conductor having a plurality of collection openings
therein to collect hydrocarbon resources from adjacent portions of
the subterranean formation; and wherein said choke fluid dispenser
is positioned in spaced relation from the collection openings.
10. A system for heating a hydrocarbon resource in a subterranean
formation having a wellbore extending therein, the system
comprising: an elongate radio frequency (RF) antenna configured to
be positioned within the wellbore and having a proximal end and a
distal end separated from the proximal end; and a choke fluid
dispenser to be coupled to a choke fluid source and positioned to
selectively dispense choke fluid into adjacent portions of the
subterranean formation at the proximal end of said RF antenna to
define a common mode current choke at the proximal end of said RF
antenna.
11. The system of claim 10 wherein said RF antenna comprises a
cylindrical conductor; and further comprising an RF transmission
line extending at least partially within said cylindrical conductor
and coupling said RF source to said RF antenna.
12. The system of claim 11 wherein said choke fluid dispenser is
carried by said transmission line and comprises: an inner sleeve
surrounding said RF transmission line; a liner surrounding said
inner sleeve and defining a first annular chamber therewith, said
liner having a plurality of ports therein in fluid communication
with the choke fluid source; and an outer sleeve surrounding said
liner and defining a second annular chamber therewith to receive
choke fluid from the plurality of ports, said outer sleeve having a
plurality of openings therein to pass choke fluid from the annular
chamber into the subterranean formation adjacent the antenna.
13. The system of claim 12 wherein said inner sleeve is slidably
movable with respect to said liner; and wherein said liner is fixed
to said outer sleeve.
14. The system of claim 10 wherein said choke fluid dispenser
further comprises a respective seal at each opposing end of said
inner sleeve.
15. The system of claim 10 wherein said RF antenna comprises a
cylindrical conductor having a plurality of collection openings
therein to collect hydrocarbon resources from adjacent portions of
the subterranean formation; and said choke fluid dispenser is
positioned in spaced relation from the collection openings.
16. A choke fluid dispenser for use with an elongate radio
frequency (RF) antenna configured to be positioned within a
wellbore in a subterranean formation and having a proximal end and
a distal end separated from the proximal end, where the proximal
end is to be coupled with an RF source via an RF transmission line,
the choke fluid dispenser comprising: an inner sleeve surrounding
the RF transmission line; a liner surrounding said inner sleeve and
defining a first annular chamber therewith, said liner having a
plurality of ports therein to be placed in fluid communication with
a choke fluid source; and an outer sleeve surrounding said liner
and defining a second annular chamber therewith to receive choke
fluid from the plurality of ports, said outer sleeve having a
plurality of openings therein to pass choke fluid from the annular
chamber into the subterranean formation adjacent the proximal end
of the RF antenna.
17. The choke fluid dispenser of claim 16 wherein said inner sleeve
is slidably movable with respect to said liner; and wherein said
liner is fixed to said outer sleeve.
18. The choke fluid dispenser of claim 16 further comprising a
respective seal at each opposing end of said inner sleeve.
19. A method for heating a hydrocarbon resource in a subterranean
formation having a wellbore extending therein, the method
comprising: applying radio frequency (RF) power to an elongate RF
antenna positioned within the within the wellbore using an RF
source, the elongate RF antenna having a proximal end and a distal
end separated from the proximal end; and selectively dispensing
choke fluid from a choke fluid source into adjacent portions of the
subterranean formation via a choke fluid dispenser positioned in
the wellbore at the proximal end of the RF antenna to define a
common mode current choke at the proximal end of the RF
antenna.
20. The method of claim 19 wherein the choke fluid comprises an
electrical conductivity enhancing fluid.
21. The method of claim 19 wherein the choke fluid comprises
water.
22. The method of claim 19 wherein the RF antenna comprises a
cylindrical conductor coupled to the RF antenna via an RF
transmission line extending at least partially within the
cylindrical conductor.
23. The method of claim 22 wherein the choke fluid dispenser is
positioned on the transmission line.
24. The method of claim 23 wherein the choke fluid dispenser
comprises: an inner sleeve surrounding the RE transmission line; a
liner surrounding the inner sleeve and defining a first annular
chamber therewith, the liner having a plurality of ports therein in
fluid communication with the choke fluid source; and an outer
sleeve surrounding the liner and defining a second annular chamber
therewith to receive choke fluid from the plurality of ports, the
outer sleeve having a plurality of openings therein to pass choke
fluid from the annular chamber into the subterranean formation
adjacent the antenna.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of hydrocarbon
resource recovery, and, more particularly, to hydrocarbon resource
recovery using RF heating.
BACKGROUND OF THE INVENTION
[0002] Energy consumption worldwide is generally increasing, and
conventional hydrocarbon resources are being consumed. In an
attempt to meet demand, the exploitation of unconventional
resources may be desired. For example, highly viscous hydrocarbon
resources, such as heavy oils, may be trapped in tar sands where
their viscous nature does not permit conventional oil well
production. Estimates are that trillions of barrels of oil reserves
may be found in such tar sand formations.
[0003] In some instances these tar sand deposits are currently
extracted via open-pit mining. Another approach for in situ
extraction for deeper deposits is known as Steam-Assisted Gravity
Drainage (SAGD). The heavy oil is immobile at reservoir
temperatures and therefore the oil is typically heated to reduce
its viscosity and mobilize the oil flow. In SAGD, pairs of injector
and producer wells are formed to be laterally extending in the
ground. Each pair of injector/producer wells includes a lower
producer well and an upper injector well. The injector/production
wells are typically located in the pay zone of the subterranean
formation between an underburden layer and an overburden layer.
[0004] The upper injector well is used to typically inject steam,
and the lower producer well collects the heated crude oil or
bitumen that flows out of the formation, along with any water from
the condensation of injected steam. The injected steam forms a
steam chamber that expands vertically and horizontally in the
formation. The heat from the steam reduces the viscosity of the
heavy crude oil or bitumen which allows it to flow down into the
lower producer well where it is collected and recovered. The steam
and gases rise due to their lower density so that steam is not
produced at the lower producer well and steam trap control is used
to the same effect. Gases, such as methane, carbon dioxide, and
hydrogen sulfide, for example, may tend to rise in the steam
chamber and fill the void space left by the oil defining an
insulating layer above the steam. Oil and water flow is by gravity
driven drainage, into the lower producer well.
[0005] Operating the injection and production wells at
approximately reservoir pressure may address the instability
problems that adversely affect high-pressure steam processes. SAGD
may produce a smooth, even production that can be as high as 70% to
80% of the original oil in place (OOIP) in suitable reservoirs. The
SAGD process may be relatively sensitive to shale streaks and other
vertical barriers since, as the rock is heated, differential
thermal expansion causes fractures in it, allowing steam and fluids
to flow through. SAGD may be twice as efficient as the older cyclic
steam stimulation (CSS) process.
[0006] Many countries in the world have large deposits of oil
sands, including the United States, Russia, and various countries
in the Middle East. Oil sands may represent as much as two-thirds
of the world's total petroleum resource, with at least 1.7 trillion
barrels in the Canadian Athabasca Oil Sands, for example. At the
present time, only Canada has a large-scale commercial oil sands
industry, though a small amount of oil from oil sands is also
produced in Venezuela. Because of increasing oil sands production,
Canada has become the largest single supplier of oil and products
to the United States. Oil sands now are the source of almost half
of Canada's oil production, although due to the 2008 economic
downturn work on new projects has been deferred, while Venezuelan
production has been declining in recent years. Oil is not yet
produced from oil sands on a significant level in other
countries.
[0007] U.S. Published Patent Application No. 2010/0078163 to
Banerjee et al. discloses a hydrocarbon recovery process whereby
three wells are provided, namely an uppermost well used to inject
water, a middle well used to introduce microwaves into the
reservoir, and a lowermost well for production. A microwave
generator generates microwaves which are directed into a zone above
the middle well through a series of waveguides. The frequency of
the microwaves is at a frequency substantially equivalent to the
resonant frequency of the water so that the water is heated.
[0008] Along these lines, U.S. Published Application No.
2010/0294489 to Dreher, Jr. et al. discloses using microwaves to
provide heating. An activator is injected below the surface and is
heated by the microwaves, and the activator then heats the heavy
oil in the production well. U.S. Published Application No.
2010/0294489 to Wheeler et al. discloses a similar approach.
[0009] U.S. Pat. No. 7,441,597 to Kasevich discloses using a radio
frequency generator to apply RF energy to a horizontal portion of
an RF well positioned above a horizontal portion of an oil/gas
producing well. The viscosity of the oil is reduced as a result of
the RF energy, which causes the oil to drain due to gravity. The
oil is recovered through the oil/gas producing well.
[0010] Unfortunately, long production times, for example, due to a
failed start-up, to extract oil using SAGD may lead to significant
heat loss to the adjacent soil, excessive consumption of steam, and
a high cost for recovery. Significant water resources are also
typically used to recover oil using SAGD, which impacts the
environment. Limited water resources may also limit oil recovery.
SAGD is also not an available process in permafrost regions, for
example.
[0011] Despite the existence of systems that utilize RF energy to
provide heating, such systems suffer from the inevitable high
degree of electrical near field coupling that exists between the
radiating antenna element and the transmission line system that
delivers the RF power to the antenna, resulting in common mode
current on the outside of the transmission line. Left unchecked,
this common mode current heats unwanted areas of the formation,
effectively making the transmission line part of the radiating
antenna. One system which may be used to help overcome this problem
is disclosed in U.S. application Ser. No. 14/167,039 filed Jan. 29,
2014, which is also assigned to the present Applicant and is hereby
incorporated herein in its entirety by reference. This reference
discloses a system for heating a hydrocarbon resource in a
subterranean formation having a wellbore extending therein which
includes a radio frequency (RF) antenna configured to be positioned
within the wellbore, an RF source, a cooling fluid source, and a
transmission line coupled between the RF antenna and the RF source.
A plurality of ring-shaped choke cores may surround the
transmission line, and a sleeve may surround the ring-shaped choke
cores and define a cooling fluid path for the ring-shaped choke
cores in fluid communication with the cooling fluid source.
[0012] Despite the advantages of such systems, further approaches
to common mode current mitigation may be desirable in some
circumstances.
SUMMARY OF THE INVENTION
[0013] A system for heating a hydrocarbon resource in a
subterranean formation having a wellbore extending therein may
include a radio frequency (RF) source, a choke fluid source, and an
elongate RF antenna configured to be positioned within the wellbore
and coupled to the RF source, with the elongate RF antenna having a
proximal end and a distal end separated from the proximal end. The
system may also include a choke fluid dispenser coupled to the
choke fluid source and positioned to selectively dispense choke
fluid into adjacent portions of the subterranean formation at the
proximal end of the RF antenna to define a common mode current
choke at the proximal end of the RF antenna.
[0014] More particularly, the choke fluid may comprise an
electrical conductivity enhancing fluid, such as water, for
example. Furthermore, the RF antenna may include a cylindrical
conductor, and the system may further include an RF transmission
line extending at least partially within the cylindrical conductor
and coupling the RF source to the RF antenna. Furthermore, the
choke fluid dispenser may be carried by the transmission line and
include an inner sleeve surrounding the RF transmission line, a
liner surrounding the inner sleeve and defining a first annular
chamber therewith, the liner having a plurality of ports therein in
fluid communication with the choke fluid source, and an outer
sleeve surrounding the liner and defining a second annular chamber
therewith to receive choke fluid from the plurality of ports. The
outer sleeve may have a plurality of openings therein to pass choke
fluid from the annular chamber into the subterranean formation
adjacent the antenna. Moreover, the inner sleeve may be slidably
movable with respect to the liner, and the liner may be fixed to
the outer sleeve.
[0015] The choke fluid dispenser may further include a respective
seal at opposing ends of the inner sleeve. The RF antenna may
comprise a cylindrical conductor having a plurality of collection
openings therein to collect hydrocarbon resources from adjacent
portions of the subterranean formation, and the choke fluid
dispenser may be positioned in spaced relation from the collection
openings.
[0016] A related choke fluid dispenser, such as the one described
briefly above, and method for heating a hydrocarbon resource in a
subterranean formation having a wellbore extending therein are also
provided. The method may include applying radio frequency (RF)
power to an elongate RF antenna positioned within the wellbore
using an RF source, the elongate RF antenna having a proximal end
and a distal end separated from the proximal end. The method may
further include selectively dispensing choke fluid from a choke
fluid source into adjacent portions of the subterranean formation
via a choke fluid dispenser positioned in the wellbore at the
proximal end of the RF antenna to define a common mode current
choke at the proximal end of the RF antenna.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic diagram, partially in section, of a
system for heating a hydrocarbon resource in accordance with an
example embodiment including a choke fluid dispenser.
[0018] FIG. 2 is a side view of the downhole antenna portion of the
system of FIG. 1 illustrating a region of desiccation adjacent the
RF antenna.
[0019] FIGS. 3(a)-3(f) are a series of time-lapsed simulated
cross-sectional views of the desiccation region of FIG. 2
demonstrating changes to the desiccation region over a time period
of operation of the RF antenna.
[0020] FIGS. 4(a)-4(c) are side and cross-sectional views of the
choke fluid dispenser of the system of FIG. 1 illustrating example
choke fluid dispensing portions thereof.
[0021] FIGS. 5(a)-5(c) are side and cross-sectional views of the
choke fluid dispenser of the system of FIG. 1 illustrating example
end attachment and sealing configurations thereof.
[0022] FIG. 6 is a side view, partially in section, of the choke
fluid dispenser of the system of FIG. 1 as carried around the
transmission line to allow relatively movement to accommodate
thermal expansion.
[0023] FIG. 7 is a perspective sectional view of the choke fluid
dispenser and RF transmission line of the system of FIG. 1
illustrating the various components and annuli therein.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0024] The present invention will now be described more fully
hereinafter with reference to the accompanying drawings, in which
embodiments of the invention are shown. This invention may,
however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein. Rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to like
elements throughout.
[0025] Referring initially to FIG. 1, a system 30 for heating a
hydrocarbon resource 31 (e.g., oil sands, etc.) in a subterranean
formation 32 having a wellbore therein is first described. In the
illustrated example, the wellbore is a laterally extending
wellbore, although the system 30 may be used with vertical or other
wellbores in different configurations. The system 30 further
includes a radio frequency (RF) source 34 for an RF antenna or
transducer 35 that is positioned in the wellbore adjacent the
hydrocarbon resource 31. The RF source 34 is illustratively
positioned above the subterranean formation 32, and may be an RF
power generator, for example. In an exemplary implementation, the
laterally extending wellbore may extend several hundred meters (or
more) within the subterranean formation 32. Moreover, a typical
laterally extending wellbore may have a diameter of about fourteen
inches or less, although larger wellbores may be used in some
implementations. Although not shown, in some embodiments a second
or producing wellbore may be used below the wellbore, such as would
be found in a SAGD implementation, for collection of petroleum,
bitumen, etc., released from the subterranean formation 32 through
heating.
[0026] Referring additionally to FIG. 7, a coaxial transmission
line 38 extends within the wellbore 33 between the RF source 34 and
the RF antenna 35. The transmission line 38 includes an inner
conductor 36 and an outer conductor 37. In some embodiments, one or
more radial support members (not shown) may be positioned between
the inner and outer conductors. The radial support members may have
openings therein which may be used to route tubes 40 for fluid, gas
flow, etc. For example, the space between the inner conductor 36
and the outer conductor 37 may be filled with an insulating gas,
such as nitrogen, if desired. Moreover, the tubes 40 may also be
used to deliver fluids such as a solvent to be dispensed in the pay
zone where the hydrocarbon resource 31 is located, for example.
[0027] A drill tubular 42 (e.g., a metal pipe) surrounds the outer
conductor 37 and may be supported by spacers (not shown). A space
between the outer conductor 37 and the drill tubular 42 defines a
passageway 43 which may be used for returning reservoir fluid
(e.g., bitumen) back to the surface, for example, to a well head
51, if desired. In such a configuration, proximal and/or distal
slotted liner portions 53, 56 of the antenna 35 would include a
plurality of collection openings 80 therein to collect hydrocarbon
resources 31 from adjacent portions of the subterranean formation
32, and the choke fluid dispenser 60 may be positioned in spaced
relation (i.e., up hole) from the collection openings as shown,
such as adjacent the heel of the antenna 35.
[0028] However, it should be noted that the illustrated
configuration need not be used for production in all embodiments,
and that the passageway 43 could be used for other purposes, such
as to supply other fluids (e.g., cooling fluid, etc.), or remain
unused. Further details regarding exemplary transmission line 38
support and interconnect structures which may be used in the
configurations provided herein may be found in co-pending
application Ser. No. 13/525,877 filed Jun. 18, 2012, and Ser. No.
13/756,756 filed Feb. 1, 2013, both of which are assigned to the
present Applicant and are hereby incorporated herein in their
entireties by reference.
[0029] A surface casing 51 and an intermediate casing 52 may be
positioned within the wellbore as shown. In the illustrated example
the RF antenna 35 is coupled with the intermediate casing 52, and
the RF antenna illustratively includes a proximal slotted liner
portion 53, a center isolator 55 (i.e., a dielectric) coupled to
the proximal slotted liner portion, and a distal slotted liner
portion 56 coupled to the center isolator opposite the proximal
slotted liner portion. The proximal slotted liner portion 53 and
distal slotted liner portion 56 are cylindrical conductors (e.g.,
metal) in the illustrated example, and the RF transmission line 38
extends at least partially within the proximal slotted liner
portion and couples the RF source 34 to the RF antenna 35. By way
of example, an electromagnetic heating (EMH) tool head 58 may be
carried by the drill tubular 42 to plug the transmission line 38
into the antenna 35 when the transmission line is inserted into the
wellbore. In the illustrated example, the EMH tool head 58 includes
a guide string attachment 59, although other EMH or antenna
attachment arrangements may be used in different embodiments.
[0030] The RF source 34 may be used to differentially drive the RF
antenna 35. That is, the RF antenna 35 may have a balanced design
that may be driven from an unbalanced drive signal. Typical
frequency range operation for a subterranean heating application
may be in a range of about 100 kHz to 10 MHz, and at a power level
of several megawatts, for example. However, it will be appreciated
that other configurations and operating values may be used in
different embodiments. The transmission line 38 and tubular 42 may
be implemented as a plurality of separate segments which are
successively coupled together and pushed or fed down the
wellbore.
[0031] The system 30 further illustratively includes a choke fluid
dispenser 60 coupled to the transmission line 38 adjacent the RF
antenna 35 within the wellbore. The RF antenna 35 may be installed
in the well first, followed by the transmission line (and choke
assembly 60) which is plugged into the antenna via the EMH tool
head 59, thus connecting the transmission line to the antenna.
Further details on an exemplary antenna structure which may be used
with the embodiments provided herein is set forth in co-pending
application Ser. No. 14/076,501 filed Nov. 11, 2013, which is also
assigned to the present Applicant and is hereby incorporated herein
in its entirety by reference. However, it should be noted that in
some embodiments the RF antenna assembly may be connected to the
transmission line at the wellhead and both fed into the wellbore at
the same time, as will be appreciated by those skilled in the
art.
[0032] Generally speaking, the choke fluid dispenser 60 is used for
common mode suppression of currents that result from feeding the RF
antenna 35. More particularly, the choke fluid dispenser 60 may be
used to confine much of the current to the RF antenna 35, rather
than allowing it to travel back up the outer conductor 37 of the
transmission line, for example, to thereby help maintain volumetric
heating in the desired location while enabling efficient, and
electromagnetic interference (EMI) compliant operation.
[0033] By way of background, because the wellbore diameter is
constrained, the radiating antenna 35 and transmission line 38 are
typically collinearly arranged. However, this results in
significant near field coupling between the antenna 35 and outer
conductor 37 of the transmission line 38. This strong coupling
manifests itself in current being induced onto the transmission
line 38, and if this current is not suppressed, the transmission
line effectively becomes an extension of the radiating antenna 35,
heating undesired areas of the geological formation 32. The choke
fluid dispenser 60, which in the illustrated example is carried on
the drill tubular 42, advantageously performs the function of
attenuating the induced current on the transmission line 38,
effectively confining the radiating current to the antenna 35
proper, where it performs useful heating.
[0034] More particularly, a choke fluid that is conductivity
enhancing liquid, such as saline or fresh water, is delivered
(e.g., in a continuous or repetitive fashion) from the choke fluid
source 50 to the choke fluid dispenser 60 via a supply line 61 at
the heel or proximal end of the antenna 35 and is allowed to infuse
into the reservoir 32. This maintains a relatively high electrical
conductivity up hole from the antenna 35 and "pins" the electric
field to this location. While the RF heating may steam water at
this location in some instances, this may be overcome by the
continuing supply of choke fluid which helps block the advance of
the RF fields beyond the location of the choke fluid dispenser 60.
Considered alternatively, the choke fluid dispenser 60 effectively
converts the reservoir 32 into a dissipative broadband choke.
[0035] The foregoing will be further understood with reference to
FIGS. 2 and 3(a)-3(f), in which a desiccation region or front 65
forms where the RF heating from the antenna 35 dries or desiccates
the formation. The series of time-lapse simulations in FIGS.
3(a)-3(f) illustrates how this desiccation region 65 grows over the
course of operation of the RF antenna 35 over weeks and months. In
the illustrated example, the simulation in FIG. 3(a) corresponds to
the start of the RF heating, while the simulation in FIG. 3(f)
represents the desiccation region 65 approximately two months
later. Power dissipation at the choke fluid dispenser 60 location
(here the heel of the antenna 35) is minimal while the tip of the
antenna has direct electrical contact with the reservoir (i.e., it
is not desiccated and the formation 32 has wet contact with the tip
of the antenna). Yet, as operation of the antenna 35 continues and
the desiccation region 65 grows over time, this increases the
resistivity of the formation 32 adjacent the antenna 35, which
causes common mode current to begin to couple to the outer
conductor 37 and flow back up the transmission line 38. However,
continued use of the choke fluid dispenser 60 over time as the RF
antenna 35 is operated advantageously keeps the desiccation region
65 from advancing back up hole past the heel of the antenna 35.
[0036] Referring additionally to FIGS. 4(a)-7, an example
implementation of the choke fluid dispenser 60 is now described. In
the illustrated example, the choke fluid dispenser 60 is carried by
the drill tubular 42/transmission line 38 assembly and includes an
inner sleeve 70 surrounding the drill tubular 42, a liner 71
surrounding the inner sleeve and defining a first annular chamber
72 therewith. The liner 71 has a plurality of ports 73 therein in
fluid communication with the choke fluid source 50, as seen in FIG.
4(c). Furthermore, an outer sleeve 74 surrounds the liner 71 and
defines a second annular chamber 75 therewith to receive choke
fluid from the plurality of ports 73. The outer sleeve 71 has a
plurality of openings 76 therein (see FIG. 4(c)) to pass choke
fluid from the annular chamber 75 into the subterranean formation
32 adjacent the antenna 35, as described above. In some
embodiments, a sand control screen(s) 79 (e.g., a Facsrite screen)
may optionally be used to keep sand from entering the first annular
chamber 72, as seen in FIG. 4(c). In the illustrated embodiment,
the screen 79 is positioned within the ports 73, but they may be
located elsewhere in different embodiments. Moreover, other
industry standard sand control approaches or configurations may
also be used in different embodiments, as will be appreciated by
those skilled in the art.
[0037] Moreover, to accommodate for thermal expansion, the inner
sleeve 70 may be slidably movable with respect to the liner 71, and
the liner may be fixed to the outer sleeve 74, as perhaps best seen
in FIG. 6. Thus, as the drill tubular 42/transmission line 38
assembly and liner 70 move along the wellbore based upon thermal
expansion (as indicated by the two-headed arrow in FIG. 6), the
first annular chamber 72 will always be in alignment with the ports
73, so that the choke fluid will continue to flow into the second
annular chamber 75 despite the relative movement of the inner
sleeve 70 with respect to the liner 71.
[0038] The choke fluid may enter the first annular chamber 72 via a
connection tube 81, as seen in FIGS. 5(b) and 6. A relatively small
diameter tube (e.g., 3/4'') may be used as the fluid line 61 to
feed choke fluid from the choke fluid source 50 at the wellhead to
the connection tube 81. The choke fluid dispenser may further
include a respective seal 77 (e.g., a chevron seal(s)) and seal nut
78 at opposing ends of the inner sleeve 70, as seen in FIGS.
5(a)-(c). However, other suitable connection or sealing
arrangements may be used in different embodiments, as will be
appreciated by those skilled in the art. Thus, during operation of
the example configuration, choke fluid is pumped into the system,
it fills the first annular chamber 72 between the inner sleeve 70
and the liner 71 between the chevron seals 77, the fluid then moves
through the screens 79 in the ports 73 and into the second annular
chamber 75, and is jetted out into the formation 32 via the holes
76.
[0039] Choke fluid dispersion into the formation 32 may be
controlled by leaving a desired spacing between the choke fluid
dispenser 60 and any collection openings 80 used for collecting
reservoir fluids, as noted above. This offset helps to define a
desired effective area where choke fluid can permeate without being
prematurely drawn back into the openings 80. This, in turn, helps
to ensure that the choke fluid provides the desired choke
functionality, before it is re-absorbed and "produced" with other
reservoir fluids. An example choke fluid flow or dispensing rate
may be between 0.1 and 10 gallons of continuous fluid flow per
minute for a typical RF heating application, although other flow
rates (and intermittent fluid flow) may be used in some
applications. In a simulated example with a 1.4 gallon per minute
flow, a total power dissipation for a 400 m antenna configuration
was 400 kilowatts for an antenna power of 4 kilowatts per meter of
antenna).
[0040] By way of comparison, a magnetic choke (such as described in
the above-noted U.S. application Ser. No. 14/167,039) may in some
implementations utilize a relatively large annular volume to
function with desired impedance, which in turn may drive larger
than standard drilling and liner sizes and increase drilling costs.
The choke fluid dispenser 60 may be relatively compact in terms of
length (e.g., it may be less than about 10 m in some applications),
while remaining compatible with standard size pipe diameters. More
particularly, drilling and completion costs typically vary with the
square of the diameter, and thus keeping the diameters as small as
possible may result in significant installation savings. Another
potential benefit of the relatively compact size of the choke fluid
dispenser 60 is that this may allow for sufficient envelope to
package a transmission line 38 with enough flow area to allow the
extension to longer or deeper implementation lengths.
[0041] Another contrast between the choke fluid dispenser 60 and a
magnetic choke is that of efficiency, in that the choke fluid
dispenser may provide for somewhat higher efficiency operation in
terms of how much input RF energy is lost during operation of the
antenna 35. The enhanced efficiency may also result in decreased
operational costs, as will be appreciated by those skilled in the
art. Moreover, magnetic chokes may generate significant heat and
accordingly require cooling via a cooling fluid circulation system,
for example, which is not the case with the choke fluid dispenser
60. The choke fluid dispenser 60 may not only provide broad band
choke performance over desired operating frequency ranges similar
to an magnetic choke, but it may also represent a savings in terms
of the number and complexity of components, and thus a potential
for additional cost savings. As a result, the choke fluid dispenser
60 may be particularly useful in "early" start-up wells used to
enhance production flow at the beginning of the recovery process,
while magnetic chokes may be more appropriate for longer term
recovery wells where enhanced tunability features may be desired
over time. However, either type of configuration may be used in
relatively short or long-term wells, and in some instances both a
magnetic choke assembly and a choke fluid dispenser may be used in
the same well, if desired.
[0042] A related method for heating the hydrocarbon resource 31 in
the subterranean formation 32 is also provided. The method may
include applying RF power to the elongate RF antenna 35 positioned
within the wellbore using the RF source 34. The method may further
include selectively dispensing choke fluid from the choke fluid
source 50 into adjacent portions of the subterranean formation 32
via the choke fluid dispenser 60 positioned in the wellbore at the
proximal end of the RF antenna 35 to define a common mode current
choke at the proximal end of the RE antenna, as discussed further
above.
[0043] Many modifications and other embodiments of the invention
will come to the mind of one skilled in the art having the benefit
of the teachings presented in the foregoing descriptions and the
associated drawings. Therefore, it is understood that the invention
is not to be limited to the specific embodiments disclosed, and
that modifications and embodiments are intended to be included
within the scope of the appended claims.
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